The first tab of the bid request is the Overview tab where you are given a brief explanation of what the bid request is for and important information about responding to the bid request. Once you are happy to continue select Next at the bottom of the page (or you can click directly onto one of the other tabs).
See the articles below for additional information on Bid Requests:
Joining and Accepting a Bid Request
Bid Request - Confirming Bid has Been Submitted
Submitting Bid Questions & Messages